LaserUser.com Forum (formerly RDWorksLab)

I now have a new replacement 80w tube and almost finished a few small jobs before I can get round to actually replacing the tube.

I'm looking for a little safety advice before I start, how can I be certain that there is no residual current around before I "cut the red wire"

Is it sufficient to disconnect the 240v mains supply from the machine, how does any residual current disipate.

Safety first

Using a well insulated screw driver while wearing eye protection carefully short the screw driver to the glass tube high voltage connection and the machine casing. Be sure YOU are not in contact with the machine casing while shorting.

Leave the machine powered down for at least half an hour would be my suggestion. Personally, I'd unplug it the night before, then change the tube in the morning.

oooh not sure I fancy that Pete, and i'll be leaving the machine off for a few days after my last pieces are cut - cheers Dave.

surely theres a way to check with a meter to ground

My process can be used to discharge the caps or to check the caps has lost their charge.
If you wait as Dave recommends there should be no charge... up I always short as a precaution....you could measure with a meter but that is effecti=ly the same as shorting to ground....I don’t think you care what the voltage may be ...just that it is not present.

True Pete, ok thats the plan ... cheers

Installed new tube, checked all water connections are good, no air trapped anywhere.

Did a few test pulses, beam is exiting the nozzle, not centred yet as I still have the realignment to do.

Took a wee video of the tube while pressing pulse, is this normal ? never actually looked before.

https://youtu.be/47bwZy4eL30

Looks like low power preionizarion zone. Normal at low power, usually straightens out once you get above a certain point. Russ talks about it every so often and has one or two videos on that specifically.

Phew - cheers Dave, I had the power set low for pulse test so sounds about right.

After I get the chance to do realignment i'll up the power and check it again

Every tube has a different threshold, so don't sweat the actual power percentage the beam finally straightens out at. I know Russ actually intentionally does some work right at the top end of the preionization zone